Electrical apparatus



April 9, 1963 R. N. WOLF ELECTRICAL APPARATUS Filed Sept. 16, 1960 IN VEN TOR. N. WOLF RICHARD By 2232 M ATTORNEY United States Patent 3,934,881 ELEUTRICAL APPARATUS Richard N. Wolf, North Billerica, Mass, assignor to Minneapolis-=i-Ioneywell Regulator Company, Minneapolis, Mind, a corporation of Delaware Filied Sept. 16, 1960, Ser. No. 56,509 17 vClaims. (Cl. 242-672) The present invention relates in general to a new and improved ribbon feed mechanism, in particular, a ribbon feed mechanism of the kind employed in a wheel-type high-speed printer.

Proper tension of the inked ribbon which is adjacent the paper web on which printing takes place is required in all printers which use such a ribbon, in order that the printed data characters be of proper quality. Uniform ribbon tension is particularly important in high-speed printers in which printing may take place at a rate upward of 1,000 lines per minute. The absence of proper ribbon tension in such a printer will result in a printed product which is smudged and the printed data characters will lack clarity and resolution.

Frequently the lack of proper ribbon tension arises from the fact that changes take place during the operation of the high-speed printer which affect the tension of the ribbon itself. One of the most common causes stems from the fact that the ribbon has a tendency to stretch in use. Such stretching may occur unevenly throughout the width of the ribbon which may be of the order of two feet and may further vary throughout the ribbon length. As a result, a certain amount of slack is produced regardless of the initial tension adjustment. In the absence of a self-correcting ribbon tensioning device, or of a device which is capable of providing more tension than is initially required and means for selectively varying the tension with a simple adjustment, the operational changes which produce ribbon slackness will result in an unsatisfactory printed product.

At the completion of a ribbon run, which may be of the order of 50 feet, a rapid, automatic reversal of the direction of ribbon travel is required without any relaxation of ribbon tension. In presently available drives, such a reversal is generally accompanied by a momentary slackness of the ribbon which results in unsatisfactory printing during a brief interval. Such ribbon feed mechanisms are generally incapable of providing a rapid response when a relaxation of ribbon tension occurs. It

additional ribbon tension may be obtained by means of a relatively simple adjustment.

"It is an additional object of this invention to provide a ribbon feed mechanism which is self-adjusting to provide constant ribbon tension under varying operating conditions. It is still another object of this invention to pro vide a reliable feed mechanism which is simple and economical in construction.

It is an additional object of this invention to provide a ribbon feed mechanism for a high-speed printer wherein the ribbon may be rapidly changed by means of a simple is a desirable feature of such a mechanism to respond to any slackening of the ribbon regardless of its origin, including slackness due to a ribbon hole, either by means of a warning signal or by disabling the printer. An efficient ribbon feed mechanism must further permit ribbon changes by means of a simple procedure capable of being carried out by relatively'unskilled personnel.

Heretofore, the ribbon feed mechanisms employed in high-speed printers for carrying out these operations have been complicated in construction, expensive to build and were generally unreliable during long periods of operation. The number and duration of the required shutdowns in the operation of such printers has been excessive in the past and has resulted in the loss of valuable time of the associated machine, such as a computer, which supplies the signals for operatingthe printer.

It is the primary object of this invention to provide a ribbon feed mechanism which overcomes the foregoing disadvantages.

It is another object of this invention to provide a mechanism for feeding the ribbon of a high-speed wheel-type printer past the print station under constant tension.

It is a further object of this invention to provide a ribbon feed mechanism for a high-speed printer wherein procedure.

It is still a further object of this invention to provide a ribbon feed mechanism for a high-speed printer which responds rapidly to a relaxation of ribbon tension and to the termination of a ribbon run.

It is another object of this invention to provide a ribbon feed mechanism wherein the ribbon tension is employed directly to facilitate the advance of the ribbon past the print station.

The invention which forms the subject matter of this application comprises a ribbon path extending from a pair of spools to a print station and past a drive roll positioned therebetween. Ribbon tension is maintained by rotating the two spools simultaneously so as to pull the ribbon in mutually opposite directions. The drive roll is rotated in a selected direction but at a slower speed, and is adapted to override the force applied by both spools. The ribbon tension is employed to maintain a pair of pinch rolls in contact with the'drive roll in order to grip the ribbon therebetween. Suitable interlocks are provided to guard against the relaxation of the ribbon tension, as well as to indicate the end of a ribbon run and to reverse the direction of the ribbon advance accordingly.

The various novel features which characterize the in vention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its advantages and specific objects thereof, reference should be had to the following detailed description and to the accompanying drawings in which:

FIGURE 1 illustrates a preferred embodiment of the invention;

FIGURE 2 illustrates an arrangement for coupling the ribbon to a permanent leader; and

FIGURE 3 illustrates one end of the ribbon which is adapted to actuate a ribbon reversing control.

With reference now to the drawings, FIGURE 1 shows a commercially available ribbon spool 10 which carries the coiled ribbon 12 thereon. A motor 14, e.g. an induction torque motor capable of having a continuous stall or counter-torque applied in normal operation without undue heat rise or mechanical damage, drives the spool 19 in a clockwise direction as indicated by the arrow in the drawing and is shown as being axially positioned with respect to the latter. A spool 16 is spaced from the spool 14 with its axis substantially parallel thereto and is driven by an induction torque motor 18 similar to the motor 14. As shown in the drawing, the motor 18 drives the spool 16 in a counterclockwise 'di rection.

The path of the ribbon 12 is seen to extend from mutually facing surfaces of the spools 1i and 16 to a print station 20. At theprint station, the ribbon 12 passes over a pair of stationary guides 22 and 24 respectively to confront the type fonts 26 of a constantly rotating print roll 28. A paper web 30 is seen to be positioned adjacent the ribbon 12. The paper web is adapted to receive an imprint on the surface which faces the ribbon, where it is driven against a selected type font 26 by the force of a type slug 32, together with the ribbon. A drive roll 34 is positioned in the ribbon path between 3 the spools 1t and '16 and the print station 20, so that the ribbon 12 diverges from the spools toward the drive roll. A motor which drives the drive roll in a selected direction at a speed less than the rotational speed of the motors 14 and 18 respectively is axially positioned with respect to the drive roll.

An arm 38 is rotatably disposed about its pivot 40 and carries a rotatable pinch roll 42 at one end. Similarly, an arm 44 is rotatably disposed about its pivot 46 and carries a rotatable pinch roll 48 at one end. Both pinch rolls are adapted to be moved into contact with the drive roll 34. A limit switch 51) is positioned adjacent the pinch roll 42 and is adapted to detect any movement of the latter tending to lift it off the drive roll 34. A limit switch 52 is positioned adjacent the pinch roll 48 so as to detect any lifting movement of the latter away from the drive roll 34.

A pair of ribbon guides 54 and 56 extend from the other ends of the arms 38 and 44 respectively, both guides being adapted to move with their respective arms. A tension spring 58 is arranged to urge the movable guides 54 and 56 toward each other and cause the facing portions of the ribbon 12 to move accordingly, A limit switch 619 is positioned between the guides 54 and 56 and is adapted to detect a mutual guide spacing less than a predetermined minimum.

The spool 16 carries a permanent ribbon leader 62 which is sufficiently long to thread through the entire unit past the print roll 28 to the spool 10. The leader is attached to the ribbon 12 by means of a tongued loop arrangement 64. The latter fulfills a dual function, as will hereinafter be explained, and is shown in detail in FIGURE 2. The permanent ribbon leader 62, of which only a portion is illustrated in FIGURE 2, is seen to terminate in a pair of loop tongues 66 which engage corresponding recessed sections 68 in the ribbon 12. Likewise, the loop tongues which terminate the ribbon engage corresponding recessed sections of the permanent leader 62. A splice key 76, shown in part, consists of a thin, plastic strap and threads the respective loop tongues. It is held in place by the ribbon tension which tends to draw the ribbon 12 and the leader 62 apart.

FIGURE 3 illustrates the ribbon 12 when the latter has been almost entirely uncoiled fromthe spool 16. A thickened ribbon portion 72 precedes the end of the ribbon and may consist of a double ribbon fold stitched together. The purpose of the thickened portion is to actuate a pinch roll limit switch, as will hereinafter be explained. 1

As previously stated, the permanent ribbon leader 62 is long enough to thread completely through the entire unit past the pinch roll 42. When the leader is extended to this position, a ribbon change may be readily effected.

Upon removal of the old spool, new spool 11 carrying the ribbon 12 which terminates in a tongued loop construction, is placed in position on its shaft. The ribbon is coupled to the leader 62 by means of splice key 70, which threads the tongued loops of both. By rotating the spool 16 in the direction of its arrow while the limit switches are temporarily deactivated, the tongued loop coupling 64 is thereupon returned to the position shown in FIGURE 1 and the apparatus is ready for operation.

Upon being energized, the meters 14 and 18 rotate the spools 1t and 16 respectively in opposite directions, each spool tending to wind up the ribbon against the force of the other. The motors are stalled and tension is imparted to the ribbon. It will be noted that this action occurs independently of any variation of the operating conditions, such as stretching of the ribbon, and that constant ribbon tension is maintained. Upon being energized, the motor 36 rotates the drive roll 34 at a lower speed than the rotational speed of the spool motors 14 and 18. The torque applied by the motor 36 is sulficient to override the action of the motors 14 and 18. Accordingly, the ribbon moves in the direction indicated by the arrow 74 at a speed determined by the drive motor. A counter-torque is applied to the ribbon by the motor 14, while the motor 18 takes up the ribbon fed from the drive roll 34 at a greater rate. As a result, ribbon tension is maintained. As previously stated, these motors are capable of having either a continuous stall or a counter-torque applied in normal operation without undue heat rise or mechanical damage.

The action of the tension spring 58 is such as to pull the movable ribbon guides 54 and 56 toward each other. The pivotal movement thus urged on the arms 38 and 44 tends to lift the pinch rolls 42 and 48 off the drive roll 34. The action of the spring 58, however, is opposed by the ribbon tension, which acts to separate the guides and to rotate the arms 38 and 44 about their respective pivots until the ribbon 12 is firmly gripped between the rotatable pinch rolls 42 and 48 respectively, and the drive roll 34. Thus, the ribbon tension is further used in lieu of separate spring means to maintain the pinch rolls 42 and 48 in contact with the drive roll and to facilitate the advance of the ribbon by providing a gripping action between the pinch rolls and the drive roll.

As previously stated, any relaxation of the ribbon tension is immediately corrected by the action of the oppositely pulling spools 10 and 16. Where the spool action is incapable of providing the proper correction, e.g. where a ribbon break has occurred, the relaxation of the ribbon tension will result in the movable, guides 54 and 56 being drawn toward each other by the spring 58 to actuate the limit switch 66. The latter may be em ployed either to give an indication of the relaxation of ribbon tension or it may be used to stop the ribbon feed entirely and to disable the printer.

By virtue of the overriding action of the drive roll 34, the ribbon 12 travels in the direction of the arrow 74 against the attempt of the motor 14 to wind the ribbon up on the spool 10. Simultaneously, the motor 18 attempts to wind up the ribbon on the spool 16 at a much faster rate than the rotation of the drive roll 34 permits. During this interval, the spool 19 acts as the supply spool, and the spool 16 acts as the take-up spool. When the ribbon 12 is almost completely uncoiled from the spool 10, the thickened portion 72 (FIGURE 3) appears and moves under the pinch roll 42 to lift the latter. The limit switch 50 is actuated and may be employed to reverse the direction of rotation of the drive roll.

Upon the reversal of the direction of rotation of the drive roll 34, the spool 16 acts as the ribbon supply spool. A counter torque is applied to it and it is rotated in a direction opposite to that in which the motor 18 tends to drive it. Similarly, the spool 10 now acts as the takeup spool and attempts to wind up the ribbon at a faster rate than the rotational speed of the drive roll 34 permits. As before, the effect of the rotation of the spools is to impart tension to the ribbon throughout its path.

When the ribbon has beenalmost completely uncofled from the spool 16, the tongued loop coupling 64 (FIG- URE .2), which constitutes a thickened portion of the ribbon, appears. As the coupling 64 rotates under the limit switch 52, the latter is actuated and effects a reversal of the direction of rotation of the drive roll 34.

It should be noted that the lift imparted to the pinch rolls by the thickened ribbon portions 72 and 64 respectively also imparts a pivotal motion to the arms 38 and 44 respectively toward the limit switch 60. The limit switch 18 so positioned, however, that the latter motion is insuflicient to actuate it and a false indication of a relaxation of the ribbon tension is not obtained. Conversely, any uncorrected relaxation of ribbon tension which actuates the limit switch 60, simultaneously actuates the limit switches 50 and 52. The latter action, however, which produces a reversal of the direction of ribbon motion, is of no consequence since the relaxation of ribbon tension is generally accompanied by a shutdown.

From the foregoing description it will be seen that the invention provides a ribbon feed mechanism which advances the ribbon 20 past the print station under great tension. The tension is self-regulating and may be controlled in a relatively simple manner merely by varying the energization of the motors 14 and 18 in order to adjust the torque applied by them. The ribbon tension itself is employed in order to supply the gripping force which permits the ribbon advance. Relatively simple controls and interlocks are provided which guard against a relaxation of the ribbon tension and eitect a prompt ribbon reversal when a spool is exhausted. Additionally, ribbon changeover is simplified in the invention herein by the relatively simple manner in which the ribbon may be spliced onto the permanent ribbon leader.

It will be readily understood that the invention is not confined to the precise embodiment illustrated in the drawings herein. Thus, the movable guides 54 and 56 need not be drawn together by means of a common tension spring, but could be independently urged toward the limit switch by a pair of separate springs, either in tension or in compression, depending on the manner in which they are positioned. Alternatively, the guides 54 and 56 could push the ribbon outwardly, under the influence of one or a pair of springs, toward a pair of correspondingly positioned limit switches which take the place of the switch 60. Similarly, the ribbon path sections need not diverge from the spools toward the drive roll as determined by the illustrated positions of the spools. The ribbon gripping arrangement is not dependent on the self-regulating tension feature discussed hereinabove. As a'consequence, it is possible to urge the pinch rolls 42 and 48 independently against the drive roll 34 without employing the tension of the ribbon for this purpose. The invention is not limited to the illustrated tongued loop arrangement for attaching the ribbon leader to the ribbon. Various arrangements are possible, e.g. the use of pressure-sensitive tape, to efiect this coupling which simultaneously provides the required ribbon thickness for actuating the limit switch.

Under certain conditions, it may be desirable to operate the spools and 16 from a single motor. This may be done either with the spools rotating in mutually opposite directions or in the same direction. Where the spools rotate in the same direction, the ribbon is coiled about one of the spools in the reverse direction from that shown. For example, the direction of rotation of the spool 16 may be reversed to a clockwise rotation if the ribbon leader 62 extends from the spool surface which is remote from the spool 10. In this case, and assuming the direction of drive roll rotation to be clockwise as shown, the clockwise rotation of the spool 16, as before, attempts to wind up the ribbon at a rate faster than is permitted by the drive roll and produces tension in the ribbon. If the direction of ribbon travel is reversed the spool 16, attempting to rotate in a clockwise direction, acts as a supply spool and has a counter-torque applied thereto by the overriding force of the drive roll which rotates in the counterclockwise direction.

A ribbon feed mechanism for a high-speed printer has thus been provided which is simple and economical in construction, and capable of self-correction under changed conditions during the operation of the apparatus which affect the ribbon tension. It will be apparent from the foregoing explanation that numerous modifications, changes and equivalents will now occur to those skilled in the art, all of which fall within the true spirit and scope contemplated by the invention.

' What is claimed is:

l. A mechanism for advancing a ribbon under tension past a print station, comprising a pair of spools spaced from each other, a drive roll positioned between said print station and said spools, the path of said ribbon consisting of a pair of sections which extend from respective ones of said spools to said print station around said intermediately positioned drive roll, said path sections converging on opposite sides of said drive roll, a pair of spaced pinch rolls, means responsive to the tension of said ribbon for urging said pinch rolls toward said drive roll to grip said ribbon therebetween, means for simultaneously rotating said spools so as to pull said ribbon in opposite directions with substantially equal forces, means for independently rotating said drive roll in a selected direction at a single peripheral speed less than that of said spools, said drive roll rotation means being adapted to override said spool rotation means to advance said ribbon in said selected direction along its \path at said drive roll speed.

2. A mechanism for advancing a ribbon under tension past a print station, comprising a pair of rotatable ribbon spools spaced from each other and adapted to provide the terminal points for said ribbon moving between said spools and said print station, a rotatable drive roll positioned in the path of said ribbon, a pair of pivotable arms positioned on opposite sides of said drive roll, and a pinch roll rotatably disposed on one end portion of each of said arms, the other end portions of said arms extending into the ribbon path between said drive roll and said print station, the ribbon tension rotating said pivotable arms to cause said pinch rolls to make contact with said drive roll and to grip the intermediately positioned ribbon.

3. A mechanism for advancing a ribbon under tension past a print station, comprising a pair of rotatable ribbon spools spaced from each other, said spools being selectively adapted to operate as supply and take-up spools respectively for said ribbon moving in a path between the latter and said print station, a drive roll positioned in said ribbon path, a pair of pivotable arms positioned on opposite sides of said drive roll, a pinch roll rotatably disposed on one side of each of said arms and being adapted to grip said ribbon in cooperation with said drive roll, the other side of each of said arms extending into said ribbon path between said drive roll and said print station, resilient means for pivoting said arms in a first direction to urge said pinch rolls out of contact with said drive roll, the ribbon tension applied to said arm extensions opposing the force of said resilient means by pivoting said arms in the opposite direction to maintain said pinch rolls in contact with said drive roll, and means responsive to the rotation of said arms in said first direction through a first predetermined angle to indicate a relaxation of ribbon tension. 7

4. The apparatus of claim 3 and further including means responsive to the angular motion of said arms in said first direction through a second predetermined angle less than said first angle adapted to efiect a reversal of the direction of rotation of said drive roll.

5. The apparatus of claim 4 and further comprising means for rotating said drive roll in a selected direction to advance said ribbon along its path, and means for simultaneously rotating said spools so as to tend to pull said ribbon in opposite directions at a peripheral speed greater than that of said drive roll, said drive roll rotation means being adapted to override said spool rotation means to advance said ribbon in said selected direction at said drive roll speed.

6. The apparatus of claim 3 and further including means for rotating said drive roll in a selected direction to advance said ribbon along its path, said ribbon including thickened portions disposed near both ends thereof adapted to lift said pinch rolls with respect to said drive roll, and means responsive to said lift adapted to effect a reversal of the direction of rotation of said drive roll.

7. The apparatus of claim 6 and further comprising means for simultaneously rotating said spools so as to tend to pull said ribbon in opposite directions at a peripheral speed greater than that of said drive roll, said drive roll rotation means being adapted to override said spool rotation means to advance said ribbon in said selected direction at said drive roll speed.

8. A mechanism for advancing a ribbon under tension past a print station, comprising a pair of rotatable ribbon spools spaced from each other, said spools being selectively adapted to operate as supply and take-up spools respectively for said ribbon moving in a path between said spools and said print station, a drive roll positioned in said ribbon path, a pair of pivotable arms positioned on opposite .sides of said drive roll, a pinch roll rotatably disposed on one side of each of said arms and adapted to grip said ribbon in cooperation with said drive roll, the other side of each of said arms extending into said ribbon path between said drive roll and said print station, resilient means for pivoting said arms in a first direction to urge said pinch rolls out of contact with said drive roll, the ribbon tension applied to said arm extensions opposing the force of said resilient means by pivoting said arms in the opposite direction to maintain said pinch rolls in contact with said drive roll, means responsive to the rotation of said arms in said first direction through a first predetermined angle to indicate relaxation of ribbon tension, means for rotating said spools so as to pull said ribbon with substantially equal force in opposite directions, and means for rotating said drive roll in a selected direction at a peripheral speed less than that of said spools, said drive roll rotation means being adapted to override said spool rotation means to advance said ribbon in said selected direction along its path at the speed of said drive roll.

9. A mechanism for advancing a ribbon under tension past a print station, comprising a pair of rotatable ribbon spools spaced from each other, said spools being selectively adapted to operate as supply and take-up spools respectively for said ribbon, a drive roll positioned substantially symmetrically between said spools and said print station, said ribbon moving in a path including a pair of sections which extend from respective ones of said spools around said drive roll to said print station, a pair of pivotable arms positioned on opposite sides of said drive roll, a pinch roll rotatably disposed on one side of each of said arms and adapted to grip said ribbon in cooperation with said drive roll, a ribbon guide extending from the other side of each of said arms into the path of said ribbon and being adapted to pinch the latter symmetrically between said drive roll and said print station, resilient means for pivotably urging said guides toward each other to move said pinch rolls out of contact with said drive roll, the ribbon tension applied to said guides forcing the latter apart in opposition to the action of said resilient means to maintain said pinch rolls in contact with said drive roll, a limit switch responsive to a predetermined minimum spacing of said guides to indicate a relaxation of ribbon tension, means for simultaneously rotating said spoolsso as to pull said ribbon with substantially equal force in opposite directions, and means for rotating said drive roll in a selected direction at a peripheral speed less than that of said spools, said drive roll rotation means being adapted to override said spool rotation means to advance said ribbon in said selected direction along its path at the speed of said drive roll.

10. A mechanism for advancing a ribbon under tension past a print station, comprising a pair of rotatable ribbon spools spaced from each other, said spools being selectively adapted to operate as supply and take-up spools respectively for said ribbon, a drive roll positioned substantially symmetrically between said spools and said print station, said ribbon moving in a path including a pair of sections which extend from respective ones of said spools around said driverolls to said print station, a pair of pivotable arms positioned on opposite sides of said drive roll, a pinch roll rotatably disposed on one side of each of said arms and adapted to grip said ribbon in cooperation with said drive roll, a ribbon guide extending from the other side of each of said arms into the path of said ribbon and being adapted to pinch the latter between said drive roll and said print station, re-

silient means for pivotally moving said guides toward each other to urge said pinch rolls out of contact with said drive roll, the ribbon tension applied to said guides forcing the latter apart in opposition-to the action of said resilient means to maintain said pinch rolls in contact with said drive roll, and a first limit switch responsive to a predetermined minimum spacing of said guides to indicate a relaxation of ribbon tension.

11. The apparatus of claim 10 and further including means for rotating said drive roll in a selected direction to advance said ribbon along its path, and second and third limit switches respectively responsive to a lifting movement of said pinch rolls relative to said drive roll.

12. The apparatus of claim 10 and further including means for rotating said drive roll in a selected direction to advance said ribbon along its path, and second and third limit switches respectively responsive to a lifting movement of said pinch rolls relative to said drive roll adapted to effect a reversal of direction of rotation of said drive roll, said lifting movement being insufficient to decrease the distance between said guides to said predetermined minimum.

13. The apparatus of claim 12 and further comprising means for simultaneously rotating said spools at a peripheral speed greater than that of said drive roll so as to pull said ribbon in opposite directions with substantially equal force, said drive roll rotation means being adapted to override said spool rotation means to advance said ribbon in said selected direction at said drive roll speed.

14. The apparatus of claim 10 and further including means for rotating said drive roll in a selected direction to advance said ribbon along its path, a ribbon leader permanently attached to one of said spools, one end of said ribbon leader and of said ribbon terminating in a plurality of corresponding tongued loops adapted to interleave with each other, a flexible key adapted to thread said loops to couple said ribbon to said leader, said coupling forming a thickened portion of said ribbon, said ribbon having another thickened portion at the other end thereof, said thickened ribbon portions being adapted to lift said pinch rolls with respect to said drive roll, and second and third limit switches respectively responsive to a lifting movement of said pinch rolls relative to said drive roll to effect a reversal of the direction of rotation of said drive roll, said lifting movement being insufl icient to decrease the distance between said guides to said predetermined minimum.

15. A mechanism for advancing a ribbon under tension past a print station, comprising, a pair of rotatable ribbon spools spaced from each other and adapted to provide the terminal points for said ribbon moving between said spools and said print station, a rotatable drive roll positioned in the path of said ribbon, a pair of rotatable pinchtrolls positioned on opposite sides of said drive roll, means responsive to the tension of said ribbon for urging said pinch rolls against said drive roll to grip the intermediately positioned ribbon, and means responsive to the motion of said pinch rolls away from said drive roll adapted to efiect a reversal of the direction of rotation of the latter.

16. A mechanism for advancing a ribbon under tension past a print station, comprising a pair of rotatable ribbon spools spaced from each other and adapted to provide the terminal points for said ribbon moving between said spools and said print station, a rotatable drive roll positioned in the path of said ribbon, at least'one pivotable arm positioned on one side of said drive roll, and a pinch roll rotatably disposed on one end portion of said arm, the other end portion of said arm extending into the ribbon path between said drive roll and said print station, the ribbon tension rotating said pivotable arm to urge said pinch roll against said drive roll and to grip the intermediately positioned ribbon.

' means to advance said ribbon in said selected direction at said single drive roll speed.

References Cited in the file of this patent UNITED STATES PATENTS Proctor July 9, Herzig Dec. 15, Roberts Feb. 9, Jones Jan. 24, Mullin Nov. 17, Axon et a1. Sept. 26, 

1. A MECHANISM FOR ADVANCING A RIBBON UNDER TENSION PAST A PRINT STATION, COMPRISING A PAIR OF SPOOLS SPACED FROM EACH OTHER, A DRIVE ROLL POSITIONED BETWEEN SAID PRINT STATION AND SAID SPOOLS, THE PATH OF SAID RIBBON CONSISTING OF A PAIR OF SECTIONS WHICH EXTEND FROM RESPECTIVE ONES OF SAID SPOOLS TO SAID PRINT STATION AROUND SAID INTERMEDIATELY POSITIONED DRIVE ROLL, SAID PATH SECTIONS CONVERGING ON OPPOSITE SIDES OF SAID DRIVE ROLL, A PAIR OF SPACED PINCH ROLLS, MEANS RESPONSIVE TO THE TENSION OF SAID RIBBON FOR URGING SAID PINCH ROLLS TOWARD SAID DRIVE ROLL TO GRIP SAID RIBBON THEREBETWEEN, MEANS FOR SIMULTANEOUSLY ROTATING SAID SPOOLS SO AS TO PULL SAID RIBBON IN OPPOSITE DIRECTIONS WITH SUBSTANTIALLY EQUAL FORCES, MEANS FOR INDEPENDENTLY ROTATING SAID DRIVE ROLL IN A SELECTED DIRECTION AT A SINGLE PERIPHERAL SPEED LESS THAN THAT OF SAID SPOOLS, SAID DRIVE ROLL ROTATION MEANS BEING ADAPTED TO OVERRIDE SAID SPOOL ROTATION MEANS TO ADVANCE SAID RIBBON IN SAID SELECTED DIRECTION ALONG ITS PATH AT SAID DRIVE ROLL SPEED. 